PROJECT SUMMARY According to the CDC, 550,000 Healthcare Associated Infections (HAIs) occur per year in the US, costing ~$100 billion and killing tens of thousands of patients. Reducing HAIs is a top priority of the US DHHS and NIH and experts have called for novel strategies including vaccination to achieve this goal. ExBaq was founded by scientists and business colleagues who have spent years studying antibiotic- resistant nosocomial pathogens. We made the striking observation that an adjuvant-only approach to activate innate immunity can provide broad-spectrum, short-term protection against lethal infection caused by a variety of HAI pathogens (preliminary data). Our triple adjuvant regimen consists of: 1) Aluminum hydroxide (Al(OH)3); 2) monophosphoryl Lipid A (MPL); and 3) Whole Glucan Particles (WGP). This triple adjuvant regimen protected mice against lethal bacteremia caused by the Gram positive pathogen, methicillin-resistant S. aureus (MRSA) and the extreme drug resistant (XDR) Gram negative pathogen, A. baumannii. In particular, WGP and MPL respectively affected Gram-positive and Gram-negative efficacy, and Al(OH)3 was required for both. Finally, preliminary data suggest that the polysaccharide, mannan, could further enhance protection. Given efficacy against Gram positive and Gram negative pathogens, our adjuvant-only vaccine has the potential to prevent HAIs caused by the highest priority, most lethal and antibiotic-resistant nosocomial pathogens in acutely hospitalized patients. The goal of this proof-of-principle Phase I STTR is to define optimal adjuvant dosing and composition to support a Phase II application that will enable GMP manufacturing, pharm-tox, and biomarker studies to support a future IND. AIM 1: Identify optimal dosing of the triple adjuvant regimen for maximal efficacy against nosocomial pathogens. We will determine if efficacy can be improved and durability prolonged by increasing adjuvant doses in mice with bacteremia or pneumonia. Mice will be vaccinated with escalating adjuvant doses or placebo and then infected IV or via the lung 7, 21, and 42 days later (covering 1, 2, and 3 STDEV of US hospital lengths of stay) with a hyper-virulent clinical blood and lung isolate of A. baumannii (HUMC1) or a USA300 clinical isolate of MRSA (LAC). The primary outcome will be time to moribund condition (death is not allowed per IACUC/NIH), with lung and/or blood bacterial burden and cytokines as secondary outcomes. AIM 2: Determine if incorporating mannan into a quadruple adjuvant further improves efficacy and/or enables lower doses of triple adjuvants to lower cost-of-goods. We will determine if adding mannan at various doses to the triple-adjuvant mixture improves efficacy and/or enables lower effective dosing. Mice will be infected IV or via the lung with A. baumannii and S. aureus. Outcome measures will be as above. These proof of principle/feasibility results will lay the groundwork for a Phase II STTR, which will focus on GMP and pharm-tox studies, as well as defining biomarkers that correlate with protection to enable IND filing.